Structures including perovskite dielectric layers and variable oxygen concentration gradient layers

ABSTRACT

Oxygen partial pressure may be controlled during annealing of a perovskite dielectric layer by providing an oxygen-absorbing layer adjacent the perovskite dielectric layer, and annealing the perovskite dielectric layer in an ambient that includes an ambient oxygen partial pressure, such that the oxygen-absorbing layer locally reduces the oxygen partial pressure adjacent the perovskite dielectric layer to below the ambient oxygen partial pressure. Thus, a perovskite dielectric layer can be annealed without the need to provide ultra-high vacuum and/or ultra-high purity ambient environments.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 10/139,454,filed May 6, 2002, entitled Methods of Controlling Oxygen PartialPressure During Annealing of a Perovskite Dielectric Layer, assigned tothe assignee of the present invention, the disclosure of which is herebyincorporated herein by reference in its entirety as if set forth fullyherein.

FIELD OF THE INVENTION

This invention relates to perovskite dielectric layers and fabricationmethods therefor, and more particularly to methods and structures forannealing perovskite dielectric layers.

BACKGROUND OF THE INVENTION

Capacitors are widely used in consumer and commercial applications. Asis well known to those having skill in the art, a capacitor generallyincludes spaced apart electrodes with a dielectric layer therebetween.

As the integration density of electronic devices continues to increase,it may become desirable to provide capacitors that have increasinglylarger capacitance-per-unit-area of an integrated circuit substrate inwhich the capacitor is used and/or of a printed circuit board or otherhigher level package in which the capacitor is used. One way to increasethe capacitance-per-unit-area is to increase the dielectric constant ofthe dielectric material.

In order to increase the dielectric constant of the dielectric material,perovskite dielectrics have been widely investigated and used. As iswell known to those having skill in the art, perovskite dielectricscomprise a class of high permittivity ceramic dielectrics having aperovskite crystal structure and include dielectric oxides, such as leadzirconate titanate (PZT) and lead lanthanum zirconate titanate (PLZT).These dielectrics may be formed into very thin flexible robust layerswith very high dielectric constants. As used herein, the term“perovskite dielectric layer” means a layer that includes one or moreperovskite dielectrics, and may also include additional non-perovskitedielectric materials.

As is well known to those having skill in the art, a perovskitedielectric layer may be annealed at a high temperature, generally higherthan about 500° C. and often at about 750° C. However, if an excessiveoxygen partial pressure, such as an oxygen partial pressure that isgreater than about 10-10 Torr, is present during the anneal, thebeneficial effects of the anneal may be reduced and/or the anneal maycause other deleterious effects on the perovskite dielectric layerand/or other layers of the capacitor, integrated circuit or higher levelpackage. Perovskite dielectric layers also may be used in many otherapplications, such as a gate insulating layer of a field effecttransistor or an interlayer dielectric layer of an integrated circuit.The above-described deleterious effects also may take place duringannealing in these other applications.

In view of the above, it is known to provide low oxygen partialpressures during annealing of a perovskite dielectric layer by vacuumannealing in an ultra-low pressure (ultra-high vacuum) environment, toobtain an oxygen partial pressure in the range of, for example, 10⁻¹⁰Torr. Unfortunately, this high vacuum annealing may be difficult and/orexpensive to maintain. It is also known to provide atmospheric orsub-atmospheric pressure annealing in an ultra-pure gas mixture havingan extremely low oxygen partial pressure in the range of, for example,10⁻¹ Torr. For example, ultra-high purity gas mixtures between CO andCO₂ and/or between H₂ and H₂O may provide sufficiently low oxygenpartial pressure. Unfortunately, significant effort and/or expense maybe needed to supply and maintain these ultra-high purity gases.

SUMMARY OF THE INVENTION

Some embodiments of the present invention control oxygen partialpressure during annealing of a perovskite dielectric layer by providingan oxygen-absorbing layer adjacent the perovskite dielectric layer, andannealing the perovskite dielectric layer in an ambient that includes anambient oxygen partial pressure, such that the oxygen-absorbing layerlocally reduces the oxygen partial pressure adjacent the perovskitedielectric layer to below the ambient oxygen partial pressure. Accordingto some embodiments of the present invention, a perovskite dielectriclayer can be annealed without the need to provide ultra-high vacuumand/or ultra-high purity ambient environments.

In other embodiments of the present invention, an acceptor-dopedperovskite dielectric layer is formed on a conductive layer thatcomprises a base metal, such as nickel or copper. The acceptor-dopedperovskite layer is annealed in an ambient that includes an ambientoxygen partial pressure, such that the conductive layer that comprises abase metal absorbs oxygen adjacent the acceptor-doped perovskitedielectric layer, to locally reduce the oxygen partial pressure in theacceptor-doped perovskite dielectric layer below the ambient oxygenpartial pressure.

Some embodiments of the present invention can provide a perovskitedielectric layer and a conductive layer that may be used as an insulatedelectrode layer and/or as an electrode and dielectric layer of acapacitor. These structures may be used in an integrated circuit, and/orin a higher level package such as a printed circuit board.

In some embodiments of the present invention, the annealing can takeplace in an ambient that includes an ambient oxygen partial pressure ofat least 10⁻⁵ Torr at temperature of at least about 500° C. In otherembodiments of the present invention, the annealing can take place in anambient that includes an ambient oxygen partial pressure of at least10⁻³ Torr at temperature of at least 500° C. In yet other embodiments ofthe present invention, the annealing takes place in an ambient thatincludes an ambient oxygen partial pressure of between 10⁻³ Torr andabout 10⁻² Torr at temperature of at least about 500° C. In otherembodiments of the present invention, the annealing takes place in anambient that includes an ambient oxygen partial pressure of betweenabout 10⁻³ Torr and about 10⁻² Torr at temperature of about 750° C. Instill other embodiments of the present invention, the annealing takesplace in a nitrogen ambient that contains about five parts per millionof oxygen. In yet other embodiments of the present invention, theannealing takes place at atmospheric pressure in a nitrogen ambient thatis obtained from a bottled nitrogen gas cylinder and/or by boiling offliquid nitrogen. In still other embodiments of the present invention,the annealing takes place such that the ambient oxygen partial pressuredoes not form an oxide of the oxygen-absorbing layer between the oxygenabsorbing layer and the perovskite dielectric layer. In yet otherembodiments of the present invention, the annealing takes place suchthat the ambient oxygen partial pressure does not oxidize theoxygen-absorbing layer adjacent the perovskite dielectric layer.

According to other embodiments of the present invention, an electronicstructure is fabricated by providing a metal foil comprising first andsecond cladding layers comprising a base metal, and a core layercomprising a base metal therebetween. A perovskite dielectric layer isformed on the first cladding layer. The perovskite dielectric layer isannealed in an ambient that includes an ambient oxygen partial pressureof at least 10⁻⁵ Torr at temperature of at least about 500° C. In otherembodiments of the present invention, annealing may take place in onethe ambients described above. Moreover, in some embodiments of thepresent invention, the core layer may comprise copper and the first andsecond cladding layers may comprise nickel. In other embodiments of thepresent invention, the core layer is substantially thicker than thefirst and second cladding layers. In still other embodiments of thepresent invention, the core layer is substantially thicker than theperovskite dielectric layer. In yet other embodiments of the presentinvention, the layer comprising perovskite dielectric layer is directlyon the first cladding layer. In still other embodiments, only a firstcladding layer is provided.

In all of the embodiments of the present invention that were describedabove, an electrode layer may be fabricated on the perovskite dielectriclayer, to produce a capacitor. In still other embodiments of the presentinvention, additional conductive and/or insulating layers may be formed.

Electronic structures according to embodiments of the present inventioninclude a perovskite dielectric layer and an oxygen-containing layerhaving a first face adjacent the perovskite dielectric layer, a secondface opposite the perovskite dielectric layer and a center regiontherebetween. The oxygen-containing layer has lower oxygen concentrationat the center region than adjacent at least one of the first and secondfaces thereof. In some embodiments of the present invention, theoxygen-containing layer has lower oxygen concentration at the centerregion than adjacent both of the first and second faces thereof. Inother embodiments of the present invention, the oxygen concentration inthe oxygen-containing layer decreases from adjacent the second face toadjacent the first face. In still other embodiments of the presentinvention, the oxygen concentration in the oxygen-containing layerdecreases from adjacent the second face to the center region and fromadjacent the first face to the center region. In some embodiments, thesedecreases may follow a functional form that is consistent with adiffusion controlled process, such as, but not limited to, exponentialdecay.

In other embodiments of the invention, the oxygen-containing layercomprises a first cladding layer comprising nickel on the perovskitedielectric layer, a core layer comprising copper on the first claddinglayer opposite the perovskite dielectric layer, and a second claddinglayer comprising nickel on the core layer opposite the first claddinglayer. In other embodiments, only a first cladding layer is provided. Insome embodiments of the present invention, the core layer includes anaverage oxygen concentration that is less than that of the secondcladding layer, and the first cladding layer includes an average oxygenconcentration that is less than that of the core layer. In otherembodiments of the present invention, the oxygen concentration decreasesacross the core layer from the second cladding layer to the firstcladding layer. In still other embodiments of the present invention, thecore layer includes an average oxygen concentration that is less thanthat of the first and second cladding layers. In yet other embodimentsof the present invention, the core layer includes a center region, andthe oxygen concentration decreases across the core layer from adjacentthe cladding layer to the center region, and from adjacent the firstcladding layer to the center region. In some embodiments, thesedecreases may follow a functional form that is consistent with adiffusion controlled process, such as, but not limited to, exponentialdecay. In still other embodiments of the present invention, a layercomprising metal also is provided on the perovskite dielectric layer, toproduce a capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 are schematic cross-sectional views of electronic structuresaccording to various embodiments of the present invention duringannealing according to various embodiments of the present invention.

FIGS. 5 and 6 are cross-sectional views of electronic structuresaccording to various embodiments of the present invention that may beformed according to various embodiments of the present invention.

FIGS. 7A and 8A are cross-sectional views of other electronic structuresthat may be formed according to various embodiments of the presentinvention.

FIGS. 7B and 8B graphically illustrate oxygen concentration profiles inthe structures of FIGS. 7A and 8A respectively, according to variousembodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying figures, in which embodiments of thepresent invention are shown. This invention may, however, be embodied inmany alternate forms and should not be construed as limited to theembodiments of the present invention set forth herein.

Accordingly, while the invention is susceptible to various modificationsand alternative forms, specific embodiments of the present invention areshown by way of example in the drawings and will herein be described indetail. It should be understood, however, that there is no intent tolimit the invention to the particular forms disclosed, but on thecontrary, the invention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the invention asdefined by the claims. Like numbers refer to like elements throughoutthe description of the figures. In the figures, the dimensions of layersand regions may be exaggerated for clarity. It will also be understoodthat when an element, such as a layer, region or substrate, is referredto as being “on” another element, it can be directly on the otherelement or intervening elements may also be present. In contrast, whenan element, such as a layer, region or substrate, is referred to asbeing “directly on” another element, there are no intervening elementspresent.

FIGS. 1-4 are schematic cross-sectional views of electronic structuresaccording to various embodiments of the present invention duringannealing according to various embodiments of the present invention.More specifically, referring to FIG. 1, an annealing chamber 120 is usedto anneal a perovskite dielectric layer 100. The annealing chamber 120may be a standard annealing furnace that is widely used in electronicdevice fabrication, and need not be described further herein. In someembodiments of the present invention, annealing temperatures of at leastabout 500° C. may be used. In other embodiments of the presentinvention, annealing temperatures of about 750° C. and annealing timesof about 30 minutes may be used.

In some embodiments of the present invention, the perovskite dielectriclayer 100 comprises lead zirconate titanate (PZT), lead lanthanumzirconate titanate (PLZT), lead lanthanide titanate (PLT), lead titanate(PT), lead zirconate (PZ), lead magnesium niobate (PMN), barium titanate(BTO), strontium titanite (STO) and/or barium strontium titanate (BSTO).In other embodiments of the present invention, the perovskite dielectriclayer 100 comprises PLZT with the formula(Pb_(1-x)La_(x))(Zr_(0.52)Ti_(0.48))O₃, where x is about 0.15. Moreover,in other embodiments of the invention, small quantities of acceptors,such as Ni, Nb, Ca and Sr may be used. In still other embodiments of thepresent invention, Ca-doped PZT with the general formulaPb_(1-x)Ca_(x+y)(Zr_(A)Ti_(B))_(1-y)O₃ where (x+y)≦15 and (a+b)=1 may beused. These perovskite dielectric layers 100 may be fabricated bychemical solution deposition (CSD), evaporation, sputtering, physicalvapor deposition, chemical vapor deposition and/or other techniques. Insome embodiments of the present invention, CSD may be used to form verythin, flexible, robust layers with very high dielectric constants. Insome embodiments of the present invention, the thickness of theperovskite dielectric layer 100 is about 1 μm. However, thicker orthinner layers may be used in other embodiments of the presentinvention.

Still referring to FIG. 1, according to some embodiments of the presentinvention, an oxygen-absorbing layer 110 is provided adjacent theperovskite dielectric layer 100. In some embodiments of the presentinvention, the oxygen-absorbing layer 110 comprises one or more basemetals, such as copper, nickel and/or alloys thereof. In otherembodiments of the present invention, the oxygen-absorbing layer 110includes a plurality of layers, as will be described below. In someembodiments of the present invention, the oxygen-absorbing layer 110 iscapable of oxidizing passively while remaining conductive. In otherwords, the oxygen-absorbing layer 110 can oxidize incompletely, allowingadditional oxygen to pass through the oxidized surface of theoxygen-absorbing layer 110. Moreover, in other embodiments of thepresent invention, the oxidized surface of the oxygen-absorbing layer110, if any, remains sufficiently conductive and thin, so as not to forman oxide of the oxygen-absorbing layer 110 between the oxygen-absorbinglayer 110 and the perovskite dielectric layer 100.

As shown in FIG. 1, according to some embodiments of the presentinvention, the perovskite dielectric layer 100 is annealed in an ambientin the annealing chamber 120 that includes an ambient oxygen partialpressure ApO₂, such that the oxygen-absorbing layer 110 locally reducesthe oxygen partial pressure adjacent the perovskite dielectric layer100, to provide a local oxygen partial pressure LpO₂ that is below theambient oxygen partial pressure ApO₂. Stated differently LpO₂<ApO₂.Moreover, in some embodiments of the present invention, LpO₂<<ApO₂. Inother embodiments of the present invention, LpO₂ is about five orders ofmagnitude less than ApO₂. In yet other embodiments of the presentinvention, ApO₂ may be at least about 10⁻³ Torr, whereas LpO₂ can be aslittle as 10⁻¹⁰ Torr. In other embodiments of the present invention,ApO₂ is between about 10⁻³ Torr and about 10⁻² Torr. In still otherembodiments of the present invention, ApO₂ is at least about 10⁻⁵ Torr.

Without wishing to be bound by any theory of operation, oxygen-absorbinglayers according to some embodiments of the present invention canprovide low local oxygen partial pressures that may be desirable inannealing perovskite dielectric layers, without the need for vacuumannealing to provide ambient oxygen partial pressures in the range of10⁻¹⁰ Torr, and without the need for atmospheric annealing in ultra-puregas mixtures having an effectively low oxygen pressure, such as in therange of 10⁻¹⁰ Torr. By providing the oxygen-absorbing layer 110adjacent the perovskite dielectric layer 100, the interaction of theoxygen-absorbing layer 110 with a medium oxygen partial pressure in theannealing chamber's ambient atmosphere can set the local oxygen partialpressure in the oxygen-absorbing layer's immediate vicinity through slowoxygen gettering. Thus, the perovskite dielectric layer 100 can residein an ambient with reduced local oxygen partial pressure LpO₂.

It will be understood that in FIGS. 1-4, the illustration of the LpO₂region surrounding the perovskite dielectric layer 100 and theoxygen-absorbing layer 110 is conceptual, and may vary in extent fromthat shown. Moreover, the demarcation between the ApO₂ region and theLpO₂ region may be gradual, rather than abrupt as shown.

In some embodiments of the present invention, the oxygen-absorbing layer1:10 may be on a substrate, such as an integrated circuit chip or ahigher level package such as a printed circuit board. In otherembodiments of the present invention, freestanding structures comprisingan oxygen-absorbing layer 110 and a perovskite dielectric layer 100 maybe annealed. Yet other combinations of layers may be annealed in otherembodiments of the present invention. Moreover, after annealing, theannealed perovskite dielectric layer may be placed in or on a substrate,such as an integrated circuit chip or a printed circuit board forincorporation therein.

FIG. 2 illustrates other embodiments of the present invention, whereinthe oxygen-absorbing layer includes a plurality of layers. Morespecifically, in FIG. 2, the oxygen-absorbing layer 210 includes a corelayer 212 comprising a base metal and first and second cladding layers214 and 216 comprising a base metal. In some embodiments of the presentinvention, the core layer comprises copper and the first and secondcladding layers 214 and 216, respectively, comprise nickel, such aselectroless nickel. In other embodiments of the present invention, thecore layer 212 may comprise one or more metals selected from copper,copper alloy, nickel and nickel alloy. In still other embodiments, onlya first cladding layer 214 may be provided.

In some embodiments of the present invention, the core layer 212 issubstantially thicker than the first and second cladding layers 214 and216. In other embodiments of the present invention, the core layer 212is substantially thicker than the perovskite dielectric layer 100. Instill other embodiments of the present invention, the first and secondcladding layers 214 and 216 are about 4 μm thick, and the core layer 212is about 17 μm thick. In other embodiments of the present invention, theperovskite dielectric layer 100 is about 1 μm thick. In still otherembodiments of the present invention, the perovskite dielectric layer100 is directly on the first cladding layer 214.

In still other embodiments of the present invention, the core layer 212is a conductive metal foil, such as a copper foil. In some embodimentsof the present invention, the first and second cladding layers 214 and216 may be deposited on the conductive metal foil by sputtering,electroless plating or electrolytic plating metals selected frompalladium, platinum, iridium, nickel phosphorus, nickel chromium and/ornickel chromium with a minor amount of aluminum. In yet otherembodiments of the present invention, the cladding layers compriseelectroless or electrolytic nickel phosphorus. The phosphorus content ofthe nickel phosphorus may generally range from about 1 to about 40weight-percent phosphorus. In other embodiments of the presentinvention, about 4-11 weight-percent phosphorus may be used. In stillother embodiments of the present invention, about 7-9 weight-percentphosphorus may be used.

In other embodiments of the present invention, the oxygen-absorbinglayer 210 comprises a copper core 212 and first and second claddinglayers 214 and 216, respectively, that comprise a nickel alloy having aconcentration of alloy ingredient that is effective to limit oxidizationof the cladding layers 214 and 216. In some embodiments of the presentinvention, concentrations between about 2% and about 9% may be used. Insome embodiments of the present invention, the cladding layers may bebetween about 1 μm and about 5 μm in thickness. In some embodiments ofthe present invention, the core 212 may be between about 20 μm and about50 μm thick. In some embodiments of the present invention, theperovskite dielectric layer 100 may be between 0.1 μm and about 1 μm inthickness. In other embodiments of the present invention, it may bebetween about 2 μm and about 4 μm of calcium-doped PLZT or PZT. It alsowill be understood that the first and second cladding layers 214 and216, respectively, need not be identical.

Various multilayer conductive foils that may be used foroxygen-absorbing layers according to embodiments of the presentinvention are described in application Ser. No. 09/629,504, filed Jul.31, 2000, entitled Multi-Layer Conductor-Dielectric Oxide Structure tothe present inventors, the disclosure of which is hereby incorporatedherein by reference in its entirety as if set forth fully herein.

FIG. 3 illustrates other embodiments of the present invention wherein anoxide 310 of the second cladding layer 216 is formed on the secondcladding layer 216 opposite the core layer 212, due to exposure to thelocal oxygen partial pressure LpO₂. As shown in FIG. 3, in someembodiments of the present invention, an oxide layer is not formedbetween the first cladding layer 214 and the perovskite dielectric layer100. Thus, the perovskite dielectric layer is directly on the firstcladding layer 214 in some embodiments of the present invention. Thehigh dielectric properties of the perovskite dielectric layer 100 may bepreserved, for example, in capacitor applications. In some embodimentsof the present invention, the oxide layer 310 may be between about 0.1μm and about 1.0 μm thick. The oxide layer 310 may be removed duringsubsequent processing if desired.

FIG. 4 illustrates other embodiments of the present invention whereinthe ambient oxygen partial pressure ApO₂ may be obtained by using aconventional nitrogen (N₂) ambient that contains about five parts permillion oxygen. More specifically, a conventional bottled nitrogen gascylinder 410 may be used. As is well known, conventional nitrogen gascylinders 410 are 99.999% pure and can have an oxygen partial pressureof between about 10⁻³ Torr and about 10⁻² Torr, so that the ambientoxygen partial pressure ApO₂ can be between about 10⁻³ and about 10⁻²Torr. Thus, in some embodiments of the invention, atmospheric pressureannealing using a conventional nitrogen gas cylinder may be used, whilestill allowing a desirably low local oxygen partial pressure LpO₂adjacent the perovskite dielectric layer 100. In yet other embodiments,liquid nitrogen may be boiled off to obtain the ambient oxygen partialpressure ApO₂.

FIGS. 5 and 6 are cross-sectional views of capacitors that arefabricated according to some embodiments of the present invention. Morespecifically, referring to FIG. 5, a perovskite dielectric layer 100 andan oxygen-absorbing layer 110 that have been annealed according toembodiments of the present invention, for example as described in FIG.1, may be further processed to form an electrode 510 thereon. Structuresof FIG. 5 may provide a capacitor, wherein the oxygen-absorbing layer110 and the electrode 510 provide the capacitor plates and theperovskite dielectric layer 100 provides the capacitor dielectrictherebetween. It will be understood that the electrode 510 may be thesame as or different from the oxygen-absorbing layer 110. In someembodiments of the present invention, the electrode 510 may comprisenickel, nickel alloy, copper, copper alloy, platinum and/or palladium.The electrode 510 may be formed on the perovskite dielectric layer 110by evaporation, sputtering, plasma deposition, chemical vapordeposition, vacuum plating, electroplating, electroless plating and/orother conventional techniques. Other embodiments of capacitor electrodesare described in the above-cited copending application to the presentinventors, and need not be described in detail herein.

FIG. 6 is a cross-sectional view of other capacitor structures that maybe fabricated according to some embodiments of the present invention. InFIG. 6, an electrode 610 is formed on the perovskite dielectric layer100 that includes a multilayer oxygen-absorbing layer 210 thereon, whichwas processed, for example, according to embodiments of the presentinvention that were described in connection with FIG. 2. The compositionof the electrode 610 may be the same as or different from the electrode510.

FIGS. 7A and 8A are cross-sectional views of electronic structures thatmay be formed according to various embodiments of the present invention.FIGS. 7B and 8B graphically illustrate oxygen concentration profiles(represented by a percentage oxygen as a function of location) in thestructures of FIGS. 7A and 8A, respectively, according to variousembodiments of the present invention. As shown in FIGS. 7A and 8A,electronic structures according to some embodiments of the presentinvention include a perovskite dielectric layer 100 and anoxygen-containing layer 710, having a first face 710 a adjacent theperovskite dielectric layer 100, a second face 710 b opposite theperovskite dielectric layer 100, and a center region 712 a therebetween.In some embodiments of the present invention, the oxygen-containinglayer 710 can include a core layer 212 and first and second claddinglayers 214 and 216, respectively, as already described.

As shown in FIGS. 7B and 8B, in some embodiments of the presentinvention, the oxygen-containing layer 710 has a lower oxygenconcentration at the center region 712 a than adjacent at least one ofthe first and second faces 710 a and 710 b thereof. In FIG. 7B, theoxygen-containing layer 710 has a lower oxygen concentration at thecenter region 712 a than adjacent the second face 710 b thereof. Incontrast, as shown in FIG. 8B, the oxygen concentration at the centerregion 712 a is lower than adjacent both the first face 710 a and thesecond face 710 b of the oxygen-containing layer 710. Moreover, as shownin FIG. 7B, in some embodiments of the present invention, the oxygenconcentration in the oxygen-containing layer 710 decreases from adjacentthe second face 710 b to adjacent the first face 710 a. In someembodiments, these decreases may follow a functional form that isconsistent with a diffusion controlled process, such as, but not limitedto, exponential decay. Finally, as shown in FIG. 8B, in otherembodiments of the present invention the oxygen concentration in theoxygen-containing layer 710 decreases from adjacent the second face 710b to the center region 712 a and from adjacent the first face 710 a tothe center region 712 a. In some embodiments, these decreases may followa functional form that is consistent with a diffusion controlledprocess, such as, but not limited to, exponential decay.

It will be understood that the center region 712 a need not be centeredbetween the first face 710 a and the second face 710 b of theoxygen-containing layer 710, and need not be symmetrical. Rather, thecenter region 712 a defines a buried region in the oxygen-containinglayer 710 that is separated from the first face 710 a and the secondface 710 b.

As shown in FIG. 7B, in some embodiments of the present invention, thecore layer 212 includes an average oxygen concentration A2 that is lessthan the average oxygen concentration Al of the second cladding layer216. Moreover, the first cladding layer 214 includes an average oxygenconcentration A3 that is less than the average oxygen concentration A2of the core layer 212. According to other embodiments of the presentinvention, and as also shown in FIG. 7B, the average oxygenconcentration decreases across the core layer 212 from adjacent thesecond cladding layer 216 to adjacent the first cladding layer 214. Insome embodiments, these decreases may follow a functional form that isconsistent with a diffusion controlled process, such as, but not limitedto, exponential decay.

Without wishing to be bound by any theory of operation, oxygenconcentration profiles as shown in FIG. 7B according to some embodimentsof the invention may arise when there is more absorption of oxygen atthe second face 710 b of the oxygen-containing layer 710 than at thefirst face 710 a. This may arise when the perovskite dielectric layer100 and/or layers formed thereon, is sufficiently thick to block atleast some absorption of oxygen from the ambient, so that more oxygen isabsorbed through the second face 710 b than from the first face 710 a.This may occur, according to some embodiments of the present invention,when the perovskite dielectric layer 100 is more than about 1.0 μmthick.

FIG. 8B illustrates other embodiments of the present invention, whereinrelatively high average oxygen concentrations are contained both in thefirst and the second cladding layers 214 and 216 relative to the corelayer 212. Without wish to be bound by any theory of operation, theseembodiments of the present invention may be produced when perovskitedielectric layer 100 is sufficiently thin, for example less than about1.0 μm, so that relatively large amounts of oxygen diffuse therethroughinto the core layer 212 through the first cladding layer 214. In theseembodiments of the present invention, as shown in FIG. 8B, the averageoxygen concentration of the core layer 212 is less than the averageoxygen concentration in both the first cladding layer 214 and the secondcladding layer 216. Stated differently, the oxygen concentration in thecore layer 212 decreases from adjacent either surface of the core layer212 towards the center region 712 a. In other embodiments of the presentinvention, the oxygen concentration decreases from adjacent the firstcladding layer 214 to the center region 712 a, and also decreases fromadjacent the second cladding layer 216 to the center region 712 a. Insome embodiments, these decreases may follow a functional form that isconsistent with a diffusion controlled process, such as, but not limitedto, exponential decay. It will be understood that the oxygenconcentration profile of FIG. 7B need not be symmetric in someembodiments of the present invention. In other embodiments of thepresent invention, a symmetric oxygen concentration profile may bepresent.

In some embodiments of the present invention, the cladding layers 214and 216 do not oxidize sufficiently to form an oxidized surface. Inother embodiments of the present invention, an oxidized surface 216a maybe formed in the second cladding layer 216, as shown in FIG. 7A, but thefirst cladding layer 214 may be free of an oxidized surface therein. Instill other embodiments of the present invention, as shown in FIG. 8A,an oxidized surface 216 a may be formed in the second cladding layer 216and an oxidized surface 214 a also may be formed in the first claddinglayer 214 a. According to still other embodiments of the presentinvention, the oxidized surface 214 a and/or 216 a can remainsufficiently conductive and thin, such that the oxygen-containing layer710 can be used as an electrode, such as a bottom electrode forcapacitors.

Additional qualitative discussion of some embodiments of the presentinvention now will be provided. Some embodiments of the presentinvention can provide oxygen-absorbing layers that can be used incombination with perovskite dielectric layers, to provide, during hightemperature annealing, a low oxygen pressure environment local to theperovskite dielectric layer in a global environment where oxygenpressure is considerably higher. This low oxygen pressure localenvironment can enhance the dielectric properties, for example incapacitor applications where loss tangent values may be reduced orminimized.

Oxygen-absorbing layers according to some embodiments of the presentinvention also may be regarded as gettering substrates. In the absenceof such a gettering substrate, complicated mechanisms may be needed toachieve the appropriate atmospheric control. These complicatedmechanisms may include annealing furnaces equipped for high vacuumprocessing and/or for controlled gas mixture, such as CO/CO₂. In someembodiments of the present invention, the gettering substrate includes amultilayer foil which can consume oxygen from the environment local tothe perovskite dielectric overlayer without self-passivation, i.e.,without forming a thin oxide skin which prevents additional oxygen fromdiffusing into the multilayer foil. In addition, in other embodiments ofthe present invention, the metal in contact with the perovskitedielectric layer may not react to form additional crystalline oramorphous products.

In some embodiments of the present invention, the multilayer foilcomprises a copper core sandwiched between two electroless nickelcladding layers. In other embodiments, only a single cladding layer maybe provided. Both copper and nickel have the capability to oxidizepassively, so that the foil can oxidize incompletely and allowadditional oxygen to pass through any oxidized surface. Moreover, anyoxidized surface can remain sufficiently conductive and thin, forexample less than about 1.0 μm thick, such that the foil can still beused as the bottom electrode for capacitors defined from the perovskitedielectric thin film. Electroless nickel is stable in contact with manyoxides at the firing temperatures of interest.

The perovskite dielectric layer may be of a composition that is tolerantof a high temperature environment with a low oxygen partial pressure. Insome embodiments of the present invention, the perovskite dielectriclayer is an acceptor-doped insulating perovskite. In other embodimentsof the present invention, the perovskite dielectric layer iscalcium-doped lead zirconate titantate, with a general chemical formulaPb_(1-x)Ca_(x+y)(Zr_(A)Ti_(B))_(1-y)O₃ where (x+y)≦15 and (a+b)=1. Whenthis type of doping is combined with a low oxygen pressure anneal, a lowloss dielectric deposited on a low cost base metal foil substrate may beprovided, according to some embodiments of the present invention.

In general, it may be highly desirable to use base metals for theconducting layers of electrical devices, such as capacitors, inductorsand/or transistors that are based upon perovskite dielectrics, forexample due to the generally lower cost of base metals in comparisonwith noble metals, such as platinum. Unfortunately, base metals may bedifficult to incorporate, since they tend to react or oxidize when incontact with commonly used perovskite dielectrics during elevatedtemperature anneals that are generally used for processing and/orintegration.

Base metals, such as nickel and copper, can be used with perovskitedielectrics, and cofired to high temperatures if the atmosphericconditions are well controlled. Specifically, if the oxygen pressure isreduced to a sufficiently low value, the base metal can survive a hightemperature anneal without oxidation, so that it does not becomeinsulating. However, many times this pressure may be sufficiently low,so as to degrade the perovskite dielectric itself.

It is known, however, that the perovskite dielectric can itself bemodified compositionally to survive this low oxygen pressure treatment.This process is commonly referred to in the capacitor industry asacceptor doping. For example, it is known to provide manganese doping ofBTO. Then, a vacuum anneal can produce an oxygen-deficient insulator, inwhich the insulating properties may be compromised, but with theappropriate acceptor doping, the low loss insulating properties ofinterest can be preserved. Thus, processing compatibility between thedissimilar materials can be achieved. Another well known example ofacceptor doping is calcium-doped lead zirconate titanate. It is knownthat, under appropriate processing conditions and stoichiometry, calciumcan substitute for titanium or zirconium. Thus, the calcium can act asan acceptor dopant, and can provide the desired defect chemistryeffects.

Low oxygen pressures are conventionally achieved by vacuum annealingand/or by atmospheric pressure annealing in a gas mixture having aneffectively low oxygen partial pressure, such as mixtures between CO andCO₂ and or mixtures between H₂ and H₂O. In either case, significanteffort and/or expense may be needed to develop and maintain suchcapability, because oxygen partial pressures in the range of 10⁻¹⁰ Torrmay be desirable.

In sharp contrast, according to some embodiments of the presentinvention, the potential benefits of base metals and perovskitedielectrics may be achieved through the use of a potentially simplerannealing equipment. According to some embodiments of the presentinvention, by having the perovskite dielectric in contact with a basemetal foil, and having the foil be much more massive than the perovskitedielectric, the interaction of the foil with the furnace atmosphere canset the oxygen partial pressure in the foil's immediate vicinity throughslow oxygen gettering. The perovskite dielectric layer, for example notmore than 1 μm in thickness, then resides in this pressure-reducedregion. Thus, in some embodiments of the present invention, anatmosphere's oxygen partial pressure may only need to be reduced to amedium level consistent with that of commonly available bottled inertgases. For example, a gas cylinder of N₂ with an impurity of 99.999%will have an oxygen partial pressure of between about 10⁻³ Torr andabout 10⁻² Torr. This level of oxygen has been experimentally determinedto be sufficiently low, so as not to over-oxidize the composite metalsubstrates. Moreover, this type of atmosphere may be achievedinexpensively.

It will be understood that much of the above description has related tothin film capacitor applications. However, oxygen-absorbing layersaccording to embodiments of the present invention may be used with otherapplications of a perovskite dielectric layer where the perovskitedielectric layer is annealed at elevated temperature in an environmentwhere low oxygen partial pressure is desired. Moreover, oxygen-absorbinglayers according to some embodiments of the present invention may beused with layers that do not comprise perovskite dielectric, where thelayers are annealed at elevated temperatures in an environment where lowoxygen partial pressure is desired.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

1. An electronic structure comprising: a perovskite dielectric layer;and an oxygen-containing layer having a first face adjacent theperovskite dielectric layer, a second face opposite the perovskitedielectric layer and a center region therebetween, the oxygen-containinglayer having lower oxygen concentration at the center region thanadjacent at least one of the first and second faces thereof.
 2. Astructure according to claim 1 wherein the oxygen-containing layer haslower oxygen concentration at the center region than adjacent both ofthe first and second faces thereof.
 3. A structure according to claim 1wherein the oxygen concentration in the oxygen-containing layerdecreases from adjacent the second face to adjacent the first face.
 4. Astructure according to claim 1 wherein the oxygen concentration in theoxygen-containing layer decreases from adjacent the second face to thecenter region and from adjacent the first face to the center region. 5.A structure according to claim 1 wherein the oxygen-containing layercomprises: a first cladding layer comprising nickel on the perovskitedielectric layer; a core layer comprising copper on the first claddinglayer opposite the perovskite dielectric layer; and a second claddinglayer comprising nickel on the core layer opposite the first claddinglayer.
 6. A structure according to claim 5 wherein the core layerincludes an average oxygen concentration that is less than that of thesecond cladding layer and the first cladding layer includes an averageoxygen concentration that is less than that of the core layer.
 7. Astructure according to claim 6 wherein the oxygen concentrationdecreases exponentially across the core layer from adjacent the secondcladding layer to adjacent the first cladding layer.
 8. A structureaccording to claim 5 wherein the core layer includes an average oxygenconcentration that is less than that of the first and second claddinglayers.
 9. A structure according to claim 8 wherein the core layerincludes a center region and wherein the oxygen concentration decreasesexponentially across the core layer from adjacent the second claddinglayer to the center region and from adjacent the first cladding layer tothe center region.
 10. A structure according to claim 1 furthercomprising a layer comprising metal on the perovskite dielectric layeropposite the oxygen-containing layer to produce a capacitor.
 11. Astructure according to claim 5 wherein the perovskite dielectric layeris directly on the first cladding layer.
 12. A structure according toclaim 11 further comprising a nickel oxide layer on the second claddinglayer opposite the core layer.
 13. A structure according to claim 5wherein the core layer is substantially thicker than the first andsecond cladding layers.
 14. A structure according to claim 5 wherein thecore layer is substantially thicker than the perovskite dielectriclayer.
 15. A structure according to claim 5 wherein the first and secondcladding layers are about 4 μm thick and wherein the core layer is about17 μm thick.
 16. A structure according to claim 1 wherein the perovskitedielectric layer comprises lead zirconate titanate.
 17. A structureaccording to claim 16 wherein the lead zirconate titanate comprisescalcium doped lead zirconate titanate.
 18. A structure according toclaim 15 wherein the perovskite dielectric layer is less than about 1 μmthick.